What happened
On January 25, 2003, a Cessna 172N, registration EC-HPH, was conducting a flight training mission for a commercial pilot course. The flight originated from Cuatro Vientos airport, traveled to Valladolid for several instrument approaches, and was on its return leg toward Cuatro Vientos when the aircraft experienced a series of engine failures.
While cruising at 8,500 feet over the Sierra de Guadarube, the engine lost power as the crew adjusted the throttle for descent. Although the crew successfully restarted the engine, a second failure occurred near the San Juan reservoir. During an attempt to land at a nearby ultralight airfield, the crew encountered another aircraft on the runway. They performed an evasive maneuver to the right, but the engine failed a final time. The aircraft struck a tree with its left wing before hitting the ground. Immediately following the impact, a fire broke out in the cabin area near the pedals, spreading rapidly to the fuel tanks and the tail section. The two occupants managed to evacuate the aircraft safely before the fire consumed the airframe.
The investigation
The investigation focused on the engine's performance and the environmental conditions at the time of the incident. Investigators examined the Lycoming O-320-H2AD engine, noting that the propeller blades showed deformations consistent with low power at impact. The inspection revealed that the carburetor was destroyed by the impact, and the oil sump had been punctured.
Investigators ruled out fuel exhaustion, as the aircraft had been refueled to capacity prior to departure and the fire confirmed the presence of fuel in the wing tanks. The ignition system and magneto functions were found to be within operational limits. The investigation also determined that the post-impact fire was caused by the left wing shifting backward upon impact, which fractured a fuel line and caused fuel to leak onto the cabin floor.
Findings
- The primary cause of the initial engine failure was likely carburetor icing, facilitated by the reduction of power and the use of a rich mixture during descent.
- Atmospheric conditions, including temperatures near 0°C and specific humidity levels, were conducive to ice formation within the induction system.
- Repeated attempts to restart the engine may have caused the engine to flood, contributing to the subsequent intermittent power and the final engine failure.
- The post-impact fire was triggered by a ruptured fuel line resulting from the structural movement of the airframe during the crash.